Color Mixing Rod Integrator in a Laser-Based Projector

ABSTRACT

The present invention provides a system ( 150 ) ( 160 ), apparatus ( 100 ) ( 200 ) and method to exploit the high beam quality of a laser light source to lower the cost and decrease the size of a color sequentially operated and laser based projector. Using a color mixing rod integrator ( 100 ) ( 200 ) ( 500 ) ( 550 ), laser light is homogenized, thus supplying the proper illumination pattern to a spatial light modulator. The rod integrator is also used to recombine the light of the primary colors, thus obviating dichroic recombination optics. For this purpose all light is coupled into the entrance plane of one and the same color mixing rod integrator. In this way a low cost and compact illumination system is obtained. By adding extra reflective layers to entrance ( 101 ) ( 201 ) and exit faces ( 105 ) of the integrator, the length of the integrator is decreased and/or the F/# in the system is increased. This enables a truly portable projector. When applying a color mixing rod integrator according to the present invention in a light engine with a reflective spatial light modulator, the integrator is very well suited for light recycling, which can increase an image&#39;s brightness up to a factor of three at average video display load.

The present invention relates to a color mixing rod integrator forilluminating a display panel in laser-based projection engines. Moreparticularly, the present invention is related to a color mixing rodintegrator that reduces laser speckle and at the same time ensureshomogeneous illumination of projected images in laser-based projectionengines.

At present the Ultra High Pressure (UHP) lamp is the most establishedlight source for rear and front projection applications, since itcombines high lumen efficacy with high source brightness at affordablecost. In the last few years solid-state light source technology hasimproved so much that it is expected to compete with UHP technology.This is because solid-state light sources offer some unique advantagessuch as high color purity, fast optical response and mercury freeoperation. The most mature solid-state light source technologyapplicable for displays is the high brightness LED that is available inall display primaries at low cost, with high lumen efficacy and with asmall form factor. However, since the light output of an LED is ratherlow and since the étendue is comparable to that of a UHP lamp, aprojector based on LEDs has low lumen output and moderate size. Hence,such projectors cannot (yet) compete with UHP lamps on applications thatrequire large screen size. However, they can very well be used in newapplication areas such as handheld and mobile projection that requirelow operating power and a compact design. However, it remains unclearwhether LED based projectors can keep up with the ever-increasingdemands of smaller size and higher lumen output.

Another type of solid-state light source, a laser, has extremely highsource brightness combined with a very small étendue. In fact, it can beconsidered to be a point source and this enables one to construct thesmallest light engine possible. It enables the design and implementationof a truly portable battery operated miniature projection display forhandheld and mobile applications. In addition, lasers are available inoutput powers that can range several Watts, thus enabling high lumenoutput. Keeping the above in mind, it is expected that lasers become theultimate light source for all types of projection applications.

However, there are some issues that impede the application of lasers indisplays. The most important of these issues are laser speckle, cost,availability in green and blue and lumen efficacy. The speckle issue isquite severe. Although the availability and lumen efficacy will probablybe solved in the foreseeable future, lasers for displays will then be atthe starting point of their learning curve, implying that the cost perlumen, coming out of a laser will still be quite high. Hence, it will bevery difficult to compete with the established UHP technology inapplications such as business to business front projection and rearprojection TV. Instead, it is much more sensible to aim at new portableprojection applications.

For these types of applications LEDs and lasers are both attractiveoptions and they will probably compete with each other mainly on theprice and size of the projector. As mentioned before, the size of alaser-based projector will be much smaller than that of an LED-basedprojector, but the price per lumen produced by a laser will be an orderof magnitude higher in the near future. In addition, even when bothtechnologies have reached their full maturity, lasers will still be moreexpensive, because the process flow for lasers requires more depositionsteps that each have to be done with a higher level of process control.

Nevertheless, the higher price per lumen does not need to be a killingbottleneck for the application of lasers in projection displays sincethere are many opportunities to lower the cost of the complete lightengine of the projector. Firstly, projectors using lasers will be morelight-efficient, implying that the required lumen output from the laseris reduced. Secondly, using an architecture with a two-dimensionalscanning mirror obviates the need for an expensive light modulator, suchas an LCoS panel. However, it is questionable whether this type ofengine can provide the needed image quality. It is also an option tolower the cost of a more or less conventional projector based on atwo-dimensional light modulator.

More recently, optical architectures using light guides have also beenproposed for HTPS transmissive- and DMD and LCoS-based reflectiveprojection engines. These proposed architectures have in common thatthey have to be combined with a light source emitting white light.

This implies that the light has to be split into three or more primarycolors and this function can be obtained by covering the exit face of anintegrator with three types of dichroic filters. Another implication ofa white light source is that color sequential operation is not possiblewithout using moving parts. Hence, these architectures are more suitedto 3-panel architectures, which intrinsically are more expensive andless compact than 1-panel architectures.

When light sources emitting light of the display primary colors areused, such as LEDs or lasers, it is possible to use frame sequentialoperation on a single display panel. In such an architecture only asingle light guide is required for homogenization of all three colors.

The present invention provides an optical system, component and methodthat exploit the high beam quality of a laser light source to lower thecost and decrease the size of a frame sequentially operated andlaser-based projector. Using a color mixing rod integrator, the presentinvention homogenizes laser light, thus supplying the properillumination pattern to a spatial light modulator. The color mixing rodintegrator is also used to recombine the light of at least two primarycolors, thus obviating the need for dichroic recombination optics. Forthis purpose all light is coupled into the entrance face 101 of one andthe same integrator, see FIG. 1.

FIG. 1 a illustrates a color mixing rod integrator that is illuminatedwith three laser sources, according to a first embodiment of the presentinvention;

FIG. 1 b illustrates the use of a color mixing rod integrator in a lightengine of a projector by proximity illumination;

FIG. 1 c illustrates the use of a color mixing rod integrator in a lightengine of a projector by applying relay optics;

FIG. 2 illustrates a first alternative embodiment of a color mixing rodintegrator component, according to the present invention;

FIG. 3 illustrates a rod integrator component with the relevant lightfluxes in the device, according to the present invention;

FIG. 4 illustrates a graph of the transmission of the color mixing rodintegrator component 100, according to the present invention, as afunction of the reflectivity of the exit face; and

FIGS. 5 a and b illustrate two alternative embodiments of the colormixing rod integrator in the present invention.

It is to be understood by persons of ordinary skill in the art that thefollowing descriptions are provided for purposes of illustration and notfor limitation. An artisan understands that there are many variationsthat lie within the spirit of the invention and the scope of theappended claims. Unnecessary detail of known functions and structure maybe omitted from the current descriptions so as not to obscure thepresent invention.

The present invention provides a system, apparatus and method wherein alight-guide is combined with at least two and most commonly three typesof laser sources that have high beam quality and emit light in thewavelength of the display primaries. The light beams are focused at theentrance holes by means of optical elements, for instance positivelenses, such that they diverge in the integrator (see FIG. 1). In thelight-guide most of the rays will hit the walls of the guide, at whichthey are reflected by means of total internal reflection (TIR). Thismechanism ensures that the light distribution at the exit face of thelight-guide is uniform and can be used to illuminate a display panel.

Please note that in FIG. 1 the distance between the beams when enteringthe integrator is quite large. In a preferred embodiment the distance isas small as possible to avoid a mismatch between the intensitydistribution of red, green and blue. Also note that the direction of thebeams is preferably perpendicular to the entrance face 101 of the colormixing rod integrator 100. Further, one or more beams at a same angle orbeams at a slightly different angle are possible to enable the beams tobe focused into the same hole. Although this results in a correct image,colored shadows can occur when the light is blocked beyond the focus.

Preferred embodiments illuminate the panel in the two alternative waysillustrated in FIGS. 1 b and c. In a first alternative 150, the colormixing rod integrator 100 is used for proximity illumination of adisplay panel 108. Since all the light is combined in a singleintegrator, this illumination system has to be combined with acolor-sequentially operated display panel, such as an LCOS panel or aDigital Mirror Device (DMD) 108. In FIG. 1 b the first alternative 150is illustrated, namely, that of illuminating an LCOS panel 108. A secondalternative 160, as illustrated in FIG. 1 c, uses the color mixing rodintegrator 100 of the present invention for illumination by means ofrelay optics 109. Note further that the second alternative 160 is morebulky than the first.

For a mobile or handheld projector, it is essential to have a smalldevice. However, in order to have sufficient homogenization in the lightguide, the majority of the light beams must have at least tworeflections at the side walls thereof. In the present invention thenumber of reflections in the color mixing rod integrator can beincreased by increasing the divergence angle θ, which is equivalent tousing a beam with a lower f-number. However, the divergence angle canonly be increased to a level that is still acceptable to the projectionlens of the system. In practice, the projection lens typically has anf-number of 2 in air (which implies an f-number of 3 in the lightintegrator when it has an index of refraction of 1.5, being typical forglass or plastic). When using the rule of thumb that the ratio of lengthand width of the integrator must be equal to twice the f-number in orderto obtain sufficient homogenization of the light distribution, theresult is an integrator length of 70 mm. Since this is rather large fora mobile projector, an alternative design for the integrator is providedin the second embodiment and is illustrated in FIG. 2.

In a second embodiment 200, part of the laser light is also allowed toreflect back towards the laser light sources. To this end, the exit face105 of the color mixing rod integrator is covered by a partiallyreflective coating 204 that is partially reflective at the wavelengthsof the laser light sources such that light incident thereon is partiallyreflected back through the integrator towards the laser sources. Inorder to prevent loss of most of the light traveling back towards thesources, the entrance face 101 of the color mixing rod integrator 200 iscovered with a highly reflective coating 202, for instance silver or amulti-layered dielectric stack, to reflect light incident thereon backtowards the exit face 105 of the color mixing rod integrator 200. Thereflection coefficient of the highly reflective coating 202 on theentrance face 101 is preferably very high. In practice, a reflectioncoefficient of at least 98% is preferred. A plurality of holes 103 haspreferably been made in the highly reflective coating 202 on theentrance face 101, each one of said plurality of holes 103 correspondingto at least one of said plurality of laser light sources. Although, onehole for all three colors is possible this decreases the throughput ofthe color mixing rod integrator 200 and is not preferred. Each hole ofthe plurality of holes 103 is of such a diameter that laser light, whichhas an extremely low étendue and thus can be focused to a very smallspot, can pass through the hole without significant light loss ordiffraction effects.

By way of example only, in FIG. 1 a a laser beam is drawn that isfocused such that it enters a color mixing rod integrator 100 with ahalf angle θ_(1/2). A beam with such a half angle can be focused to adiameter d that is given by:

$\begin{matrix}{d = {1.22\frac{\lambda}{2\; \tan \; \left( \theta_{1/2} \right)}}} & (1)\end{matrix}$

The diameter of the hole preferably exceeds this size by at least afactor of two to minimize diffraction effects.

In the embodiment illustrated in FIG. 2, although a reflective coating202 on the entrance face 101 reflects most of the light incident thereonback towards the exit face 105, some of the light will pass through theholes 103 or will be absorbed somewhere else in the system. A model ispresented below of the color mixing rod integrator 200 to determine theinfluence of the loss factors on the total optical throughput of theintegrator 200.

The light flux at different positions in the color mixing rod integrator200 is indicated in FIG. 3. In FIG. 3 the following symbols are defined:

φ₀(r) is the light flux that enters the integrator through an entrancehole 301 with relative area r (i.e. the fraction of the total area). Ofcourse, the light flux is a function of the radius of the hole. Insidethe integrator 100 200 the light flux going from left to right isdefined as φ₁ and the light flux going from right to left as ψ₁.Finally, the light flux leaving the integrator is defined as φ_(T).

The reflection coefficient of the side walls (interior surface of theintegrator) 107 is defined as unity because of total internalreflection, the reflection of the entrance face as R_(i), the reflectionof the exit face as R_(e) and the transmission of the exit face asT_(e).

The flux at different positions inside and outside the integrator cannow be described in the following set of equations:

φ₁=φ₀(r)+R _(i)(1−r)ψ₁

ψ₁=R_(e)φ₁

φ_(r)=T_(e)φ₁  (2)

The transmitted intensity is calculated by eliminating φ₁ and ψ₁:

$\begin{matrix}{\varphi_{T} = \frac{T_{e}\varphi_{0}}{1 - {\left( {1 - r} \right)R_{i}R_{e}}}} & (3)\end{matrix}$

With this formula the transmission efficiency can be calculated, whichis defined by φ_(T)/φ₀. The result of a calculation for a laser beamthat illuminates a 0.55″ WVGA HTPS transmissive LCD panel by proximityillumination is a follows:

-   -   The area of the exit face is approximately 8.4*11.2 mm².    -   The maximal F/# of the beam that is focused onto a hole 103 of        the integrator is 5. Hence, the spot diameter of the        (diffraction limited) beam is maximally 60 μm in that case,        implying that the hole diameter should be 120 μm or larger.    -   The value of r is 3·10⁻⁴ (three holes for the colors).    -   The reflection coefficient of the entrance face is varied        between 98 and 99%.

FIG. 4 illustrates a graph of the transmission of the color mixing rodintegrator 200 as a function of the reflectivity of the exit face.

In the calculation, two alternatives can be distinguished for applyingthe color mixing rod integrator:

1. In the first alternative, the beam diverges inside the integrator 500to such an extent that it fully covers the exit face of the integratorin the first pass after the integrator. The situation in which it justcovers the exit face is depicted in FIG. 5 a. Also a longer integrator(or lower f-number) is possible. A compact integrator can be obtained bychoosing a low f-number (for instance 2). From a simulation it has beendetermined that a reflection coefficient of 0.5 of the exit face and anintegrator length of 35 mm results in a homogeneous pattern at the exitface. It can be seen from FIG. 4 that the transmission of the colormixing rod integrator 500 is almost unity in that case.

2. In the second alternative the f-number is chosen to be larger thanthat of the integrator 500 of the first alternative, so that the firstpass through the color mixing rod integrator 510 results in a relativelysmall spot at the exit face. This situation is illustrated in FIG. 5 b.If the reflection coefficient of the exit face is too small, theintensity distribution at the exit face shows a bright ‘hot spot’, whichalso appears in the projected image. Therefore, the reflectioncoefficient is preferably chosen sufficiently high but not too high.From simulation it has been determined that the reflection coefficientR_(e) of the end face is preferably at least 95%, when combined with anf-number of 5 and a color mixing rod integrator length of 20 mm. In thesituation where R_(e)=95%, the throughput of the color mixing rodintegrator is 72% and 83% for R_(i)=98% and 99%, respectively. Thethroughput at R_(e)=95% is mainly determined by the loss due to thereflection of the entrance face. Hence, it is advantageous to decrease rby, for instance, placing interference filters at the entrance holes 203that only allow light of the correct wavelength to pass therethrough.

It should be noted that this second alternative for applying the colormixing rod integrator 200 of the present invention can include aprojection lens with a higher f-number. This has the advantage that itdecreases the cost and increases the depth of focus.

In both alternative embodiments of applying the color mixing rodintegrator 200 of the present invention, the light will, on the average,pass through the color mixing rod integrator 200 a plurality of times.If the path length difference of beams passing through the integrator200 a different number of times is larger than the coherence light ofthe light used, the beams do not interfere with one another. Thisresults in a laser generated image by the illumination system having adecreased speckle contrast, when compared with a system that only uses asingle pass through an integrator. It also holds that the average numberof passes determines the amount of speckle reduction. Hence, the secondalternative provides the best speckle reduction.

In the present invention:

-   -   The color mixing rod integrator comprises an optical integrator        and color mixer that together with its light source can be used        as an illumination unit in a projection engine.    -   The color mixing integrator of the present invention can be used        for proximity illumination and for illumination by means of        relay lenses. It is also possible to enlarge or decrease the        size of the exit face of an optical imaging system according to        the present invention. In case of enlargement of the exit face,        the f-number of the integrator can be made smaller, such that        the f-number at the display panel is still typically 2.    -   The panel that is illuminated can be a two-dimensional or        one-dimensional spatial light modulator. The former case is        described in detail in the foregoing discussion of embodiments.        In the latter case a planar light-guide with the shape of the        embodiments described must be used in which the thickness of the        light-guide is much smaller than the other dimensions of the        light-guide.    -   The present invention can be used to illuminate very small        display panels (below 0.5″) without a loss of light due to a        limited acceptance aperture of the system. Using a very small        display panel lowers the panel cost and at the same time        decreases the size of the illumination optics. This is an        advantage of the present invention over UHP and LED based        systems.    -   In all embodiments of the present invention discussed above, one        color per laser is used. However, this was to simplify the        discussion. It is possible for more lasers per color to be used,        such that each color has its own hole in the entrance face. The        use of more than one source per color adds to the cost, but at        the same time, decreases the speckle contrast.    -   It should be noted that the illumination schemes, as depicted in        FIGS. 1 b and 1 c both have an additional advantage of        increasing the optical efficiency of the system. The light of        the pixels in the off-state can be redirected towards the rod        integrator. Since the reflection coefficient of the exit and/or        entrance face of the integrator is quite high, most of the light        can be recycled. A quick calculation yields the result that the        peak brightness at video display load increases by a factor of        three. This results in sparkling images.    -   In order to decrease the effect of a hot spot in the image, the        reflection coefficient of the exit face of the integrator need        not be constant across the surface of the exit face.    -   The invention also applies to light engine architectures having        more than three primary colors.

While the preferred embodiments of the color mixing rod integrator ofthe present invention have been illustrated and described, it will beunderstood by those skilled in the art that the embodiments of thepresent invention as described herein are illustrative and variouschanges and modifications may be made and equivalents may be substitutedfor elements thereof without departing from the true scope of thepresent invention. In addition, many modifications may be made to adaptthe teachings of the present invention to a particular situation withoutdeparting from its central scope. Therefore, it is intended that thepresent invention not be limited to the particular embodiments disclosedas the best mode contemplated for carrying out the present invention,but that the present invention include all embodiments falling withinthe scope of the claims appended hereto as well as all implementationtechniques.

1. A color mixing rod integrator (100) (200) for a plurality of beams oflaser light of a plurality of primary display colors, comprising: arod-shaped body (106) having an interior that passes laser lighttherethrough and an interior surface (107) that reflects light incidentthereon; an entrance face (101) covered with a first reflective coating(102) to reflect light incident thereon back into the interior of therod-shaped body (106) and positioned on a first end of the rod-shapedbody having a plurality of holes (103) therein such that each hole ofsaid plurality (103) allows light of at least one beam of said pluralityof beams to pass therethrough into the interior of the rod-shaped body(106); an exit face (105) positioned on a second end of the rod-shapedbody (106) opposite to and parallel to the entrance face (101), saidexit face (105) to allow a part of light incident thereon to passtherethrough; and means for diverging each of said beams toward saidexit face (105) through said interior, wherein, part of the laser lightentering said rod integrator via said holes (103) is forced to passthrough the interior thereof several times before passing through saidexit face (105) and then exiting through said exit face (105) ishomogenized.
 2. The color mixing rod (100) (200) of claim 1, wherein therod-shaped body (106) further comprises a length greater than or equalto the coherence length of the plurality of beams of laser light suchthat said homogenized light exiting through said exit face (105) hasspeckle therein reduced.
 3. The color mixing rod (100) (200) of claim 1,wherein the laser light passing through said exit face (105) has speckletherein reduced by at least 75% and transmission thereof is greater than85%.
 4. The color mixing rod integrator (100) (200) of claim 1, whereinsaid means for diverging is a plurality of optical elements positionedat said holes (103) such that the divergence of a beam at the end of afirst pass through the integrator (100) (200) is a divergence selectedfrom the group consisting of a spot across the entire exit face (500)and a spot of a predetermined diameter on the exit face (550).
 5. Thecolor mixing rod integrator (100) (200) of claim 4, wherein: said exitface (105) is covered with a partially reflective coating (204) thatallows a part of light incident thereon to pass therethrough andreflects a part of light incident thereon back into the rod-shaped body(106) toward a source of said light; and said reflective coating (102)on said entrance face (101) is a highly reflective coating (202).
 6. Therod integrator (100) of claim 5, wherein: the first reflective coating(102) is a highly reflective material (202) selected from the groupconsisting of silver and a dielectric stack; and the plurality of holes(103) are each of a diameter such that the laser light can be focusedinto said hole and can pass therethrough without significant light lossand diffraction effects.
 7. The rod integrator (100) (200) of claim 6,wherein: said laser light is focused to enter each of the holes (103)with a half angle θ_(1/2)<20 degrees in air; each of said holes (103)has a diameter ≧2d where d is determined by the equation${d = {1.22\frac{\lambda}{2\; \tan \; \left( \theta_{1/2} \right)}}};$to minimize diffraction effects; and said second reflective coating(204) is dimensioned to have a transmission coefficient T_(e) that issignificantly lower than 50% and a reflection coefficient R_(e)=1−T_(e)such that part of the light is transmitted and part is reflected backinto the rod integrator (100) (200) thereby, wherein, the reflectedlight travels back to the entrance face (101), at which it is almostcompletely reflected for another pass through the rod integrator (100)(200) with a net effect that light exiting the rod integrator at theexit face (105) is composed of light that has passed through the rodintegrator (100) (200) at least 1 time.
 8. The rod integrator (100)(200) of claim 7, wherein said half angle θ_(1/2)<15 degrees in air. 9.A method for integrating a plurality of laser beams of light each beamcomprising one of a plurality of primary display colors, comprising:providing a rod-shaped body (106) that includes an entrance face (101)positioned on a first end and an exit face (105) positioned on a secondend (106) opposite to and parallel to the entrance face (101) and havingan interior that passes the laser beams of light therethrough and aninterior surface (107) that reflects light incident thereon back intothe interior of the rod-shaped body (106); covering the entrance face(101) of the provided rod-shaped body with a first reflective coating(102) having a plurality of holes (103) therein to allow light of saidlaser beams to pass therethrough into the interior of the rod-shapedbody, said first reflective coating to reflect light incident thereonback into the interior of the rod-shaped body (106); and diverging eachof said beams toward said exit face (105) through said interior, whereinpart of the light of said laser beams entering said rod-shaped body(106) via said holes (103) is forced to pass through the interiorthereof a plurality of times before passing through said exit face (105)and then exiting through said exit face (105), is homogenized.
 10. Themethod of claim 9, wherein said rod-shaped body (106) a length greaterthan or equal to the coherence lengths of the beams of laser light suchthat said light exiting through said exit face (105) has speckle thereinreduced.
 11. The method of claim 9, wherein said light exiting throughsaid exit face (105) has speckle therein reduced by at least 75% andtransmission thereof is greater than 85%.
 12. The method of claim 11,further comprising the step of providing a partially reflective coating(204) covering the exit face (105) that reflects a part of the lightincident thereon back into the interior of the color mixing rodintegrator (200) and allows a remaining part of the light incidentthereon to pass therethrough;
 13. The method of claim 12, wherein eachhole of the plurality of holes (103) is of such a diameter d that thebeams of laser light, which have an extremely low étendue and thus canbe focused to a very small spot, can pass through the holes (103)without significant light loss or diffraction effects.
 14. The method ofclaim 13, wherein said diverging step further comprises the step ofproviding a plurality of optical elements positioned at said holes (103)such that the divergence of a beam at the end of a first pass throughthe integrator (100) (200) is a divergence selected from the groupconsisting of a spot across the entire exit face (500) and a spot of apredetermined diameter on the exit face (550).
 15. The method of claim14, further comprising the steps of: focusing each of said beams oflight to enter a hole of said plurality of holes (103) with a half angleθ_(1/2)<20 degrees in air; sizing each said hole of said plurality ofholes (103) to have a diameter ≧2d where d is determined by the equation${d = {1.22\frac{\lambda}{2\; \tan \; \left( \theta_{1/2} \right)}}};$to minimize diffraction effects; and dimensioning said second reflectivecoating (104) to have a transmission coefficient T_(e) that issignificantly lower than 50% and a reflection coefficient R_(e)=1−T_(e)such that part of the light is transmitted and part is reflected backinto the interior of the color mixing rod integrator (100) (200)thereby, wherein, the reflected light travels back to the entrance face(101), at which it is almost completely reflected for another passthrough the color mixing rod integrator (100) (200) with a net effectthat light exiting the color mixing rod integrator (100) (200) at theexit face (105) is composed of light that has passed through the colormixing rod integrator (100) (200) at least 1 time.
 16. The method ofclaim 15, wherein said half angle θ_(1/2)<15 degrees in air.
 17. Aprojection engine (160), comprising: a color mixing rod integrator (100)(200) including: a rod-shaped body (106) having an interior that passesa plurality of beams of laser light of a plurality of primary displaycolors therethrough and an interior surface (107) that reflects lightincident thereon back into the interior of the rod-shaped body (106), anentrance face (101) positioned on a first end of the rod-shaped bodycovered with a first reflective coating (101) having a plurality ofholes (103) therein to allow the laser beams of light to passtherethrough into the interior of the rod-shaped body, said firstreflective coating to reflect light incident thereon back into theinterior of the rod-shaped body (106), means for diverging each of saidbeams of said plurality of beams toward said exit face (105) throughsaid interior, said means being positioned in proximity to saidplurality of holes (103), and an exit face (105), positioned on a secondend of the rod-shaped body (106) opposite to and parallel to theentrance face (101), wherein part of the beams of laser light enteringsaid rod integrator via said plurality of holes (103) at a given halfangle is forced to pass through the interior thereof several timesbefore passing through said exit face (105) and then exiting throughsaid exit face (105) is homogenized; a display panel (108) configured inproximity to said exit face (105) of said color mixing rod integrator(100) (200) such that illumination of said display panel (108) is by thehomogenized light exiting through said exit face (105).
 18. The engine(160) of claim 17 wherein the rod-shaped body (160) has a length greaterthan or equal to the coherence lengths of the plurality beams of laserlight of a plurality of primary display colors such that said lightexiting through said exit face (105) has speckle therein reduced. 19.The engine (160) of claim 17, wherein the beams of laser light exitingthrough said exit face (105) have speckle therein reduced by at least75% and transmission thereof is greater than 85%.
 20. The engine (150)of claim 17, further comprising a second reflective coating (204) thatis a partially reflective coating (204), covering the exit face (105),wherein, a part of the beams of laser light is reflected back toward thesources thereof by the partially reflective coating (204) and aremaining part of the beams of light exits therethrough.
 21. The engine(150) of claim 20, wherein said means for diverging is a plurality ofoptical elements positioned at said holes (103) such that the divergenceof a beam at the end of a first pass through the integrator (100) (200)is a divergence selected from the group consisting of across the entireexit face (500) and a spot of a predetermined diameter on the exit face(550).
 22. The engine (150) of claim 21, wherein said first reflectivecoating (102) on said entrance face (101) is a highly reflective coating(202).
 23. The engine (150) of claim 22, wherein: the highly reflectivecoating (202) is a material selected from the group consisting of silverand a dielectric stack; the plurality of holes (103) are each of adiameter such that each of the beams of laser light can be focused intoone of said holes (103) and can pass therethrough without significantlight loss and diffraction effects.
 24. The engine (150) of claim 23,wherein: each said beam of laser light is focused to enter one of saidholes (103) with a half angle θ_(1/2)<20 degrees in air; each of saidholes (103) has a diameter ≧2d where d is determined by the equation${d = {1.22\frac{\lambda}{2\; \tan \; \left( \theta_{1/2} \right)}}};$to minimize diffraction effects; and said second reflective coating(204) is dimensioned to have a transmission coefficient T_(e) that issignificantly lower than 50% and a reflection coefficient R_(e)=1−T_(e)such that part of the light is transmitted and part is reflected backinto the rod integrator (100) (200) thereby, wherein, the reflectedlight travels back to the entrance face (101), at which it is almostcompletely reflected for another pass through the color-mixing rodintegrator having a net effect that light exiting the color-mixing rodintegrator at the exit face (105) is composed of light that has passedthrough the color-mixing rod integrator at least 1 time.
 25. The engine(160) of claim 24, wherein said half angle θ_(1/2)<15 degrees in air.26. The engine (160) of claim 24, further comprising a relay optics 109configured in proximity to said exit face (105) to accomplishillumination of said display panel (108).